Control of cell fate and the extracellular environment are critical for tissue regeneration and cell therapy. During development, for example, cells are instructed by a complex set of microenvironmental cues, comprising soluble mediators and direct contacts with extracellular matrix and neighboring cells that are precisely regulated in time and space (Murry et al., 2008, Cell, 132:661-680). Consequently, when the microenvironmental balance is altered, cells can be activated toward homeostatic responses, such as to the regeneration of damaged tissues, or to pathologic changes in cell phenotype resulting in aberrant cell growth or loss of function.
Current methods to control cell fate in culture include: i) genetic manipulation of cells to program a desired phenotype, ii) addition of drugs or growth factors to the culture media, and iii) presentation of an engineered extracellular environment. Genetic modification has been used to program cell fate in culture to promote expression of specific cell surface receptors and to drive production of therapeutic peptides and proteins (Kumar et al., 2007, FASEB J., 21:3917-27; Haider et al., 2008, Circ. Res., 103:1300-08; Gnecchi et al., 2005, Nat. Med., 11:367-368; Gnecchi et al., 2006, FASEB J., 20:661-669; Sasportas et al., 2009, Proc. Natl. Acad. Sci. USA, 106:4822-27; Mangi et al., 2003, Nat. Med., 9:1195-1201). However, these modifications can exhibit a long-term impact on the cells, can be limited to agents that can be manufactured by cells, and aside from use of genetic switches, there may be an inability to finely tune the release kinetics of these agents.
Drugs or growth factors can be added to culture media to mimic a tissue microenvironment, however all cells typically receive essentially the same signal, and application of soluble factors for controlling the fate of transplanted cells is typically limited to pre-conditioning regimens. Alternatively, scaffolds or 2D/3D micro/nano-engineered substrates are useful to create multiple distinct microenvironments within a single culture system. These types of substrates have been used extensively to study cell-cell interactions, transplant cells, or mimic stem cell niches in vitro through support of cell proliferation, differentiation, or migration via controlled presentation of soluble cues and adhesive interactions (Lutolf et al., 2009, Nature, 462:433-4411; Discher et al.,2009, Science, 324:1673-77; Albrecht et al., 2006, Nat. Methods, 3:369-375; Mooney et al., 2008, Cell Stem Cell, 2:205-213). In addition, cues such as growth factors can be chemically immobilized to the substrate, providing specific locations to modulate cell behavior (Fan et al., 2007, Stem Cells, 25:1241-51; Davis et al., 2005, Circ. Res., 97:8-15; Luo et al., 2004, Nat. Mater., 3:249-253). However, these strategies typically require cells to be on, or in close proximity to the substrate. Engineering substrates to control cell phenotype and function often involves a complex manufacturing methodology and there are several circumstances under which it may be desirable to infuse cells in vivo without the use of a carrier or substrate (e.g., systemic cell infusion) (Karp et al., 2009, Cell Stem Cell, 4:206-216).
Thus, there is a need to exert control over cells and their microenvironment without genetic modification or the use of an engineered substrate.